<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
<style>
body {margin: 0;}
#ul1 {width: 1080px; margin: 100px auto 0;}
li { width: 247px; list-style: none; float: left; margin-right: 10px; }
li div {border: 1px solid #000; padding: 10px; margin-bottom: 10px;}
li div img { width: 225px; display: block;}
</style>
<script src="ajax.js"></script>
<script>
window.onload = function() {
	
	var oUl = document.getElementById('ul1');
	var aLi = oUl.getElementsByTagName('li');
	var iLen = aLi.length;
	var iPage = 1;
	var b = true;
	
	//初始化数据处理
	getList();
	
	function getList() {
		ajax('get','getPics.php','cpage=' + iPage,function(data) {
		
			var data = JSON.parse(data);
			
			if ( !data.length ) {
				//后续没有数据了
				return ;
			}
			
			for ( var i=0; i<data.length; i++ ) {
				
				//获取高度最短的li
				var _index = getShort();
				
				var oDiv = document.createElement('div');
				var oImg = document.createElement('img');
				oImg.src = data[i].preview;
				oImg.style.width = '225px';
				oImg.style.height =  data[i].height * ( 225 / data[i].width ) + 'px';
				oDiv.appendChild( oImg );
				var oP = document.createElement('p');
				oP.innerHTML = data[i].title;
				oDiv.appendChild( oP );
				
				aLi[_index].appendChild( oDiv );
				
			}
			
			b = true;
			
		});
	}
	
	window.onscroll = function() {
		
		var _index = getShort();
		var oLi = aLi[_index];
		
		var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
		
		if ( getTop( oLi ) + oLi.offsetHeight < document.documentElement.clientHeight + scrollTop ) {
			
			if ( b ) {
				b = false;
				iPage++;
				getList();
			}
			
		}
		
	}
	
	function getShort() {
		var index = 0;
		var ih = aLi[index].offsetHeight;
		for (var i=1; i<iLen; i++) {
			if ( aLi[i].offsetHeight < ih ) {
				index = i;
				ih = aLi[i].offsetHeight;
			}
		}
		return index;
	}
	
	function getTop(obj) {
		var iTop = 0;
		while(obj) {
			iTop += obj.offsetTop;
			obj = obj.offsetParent;
		}
		return iTop;
	}
	
}
</script>
</head>

<body>
	<ul id="ul1">
    	<li></li>
      	<li></li>
        <li></li>
        <li></li>
    </ul>
</body>
</html>
